The invention relates to a spectacle lens edge grinding machine in which in a pregrinding step the spectacle lens receives its circumferential contour, is subsequently subjected to a finishing step, especially a facet grinding step, the circumferential data of the circumferentially ground lens is determined, input into a computer, and the radial movement, and optionally the axial movement, of the spectacle lens relative to the grinding wheel is computer-controlled with the aid of the circumferential data in an optionally subsequently performed corrective grinding step with the aid of the peripheral data with the computer.
Such a device is disclosed in German Patent 40 12 660 of the assignee. In this device the data of the circumferential contour of the spectacle lens is determined and input into the computer during or after completion of the fine-grinding step with a transducer, operating contactless and arranged in a housing of the spectacle lens edge grinding machine. The determined actual values of the circumferential contour are compared within the computer with nominal values of the circumferential contour stored therein, and reaching or surpassing of a predetermined permissible deviation is detected, whereby finishing grinding is performed only upon surpassing the permissible deviation with control based on the corrective values resulting from this deviation.
Even though the principle of determining the actual values of the circumferential contour of form-ground spectacle lenses and the thus optionally resulting corrective grinding have been proven successful, it has been shown in practice that the contact-free operating transducers arranged within the housing are disadvantageously effected by the atmosphere present in the area of the spectacle lens within the housing of the spectacle lens edge grinding machine which atmosphere is loaded more or less uniformly by splashing cooling media and abrasive grit, so that it is required, when exact measuring results and exact grinding results based thereon are to be achieved, to perform a frequent cleaning.
Upon grinding the V-shaped bevel of a spectacle lens wear of the grinding wheel at the V-shaped bevel groove results which not only results in an enlargement of the finish-ground spectacle lens, but also in an increase of the acute angle of the V-shaped bevel, i.e., a flattening of the bevel. The flattening of the V-shaped bevel can be accepted to a certain extent, as long as the spectacle lens is securely held within the bevel groove of the respective spectacle frame. This requires, however, that the circumferentially ground spectacle lens is subjected to a corrective grinding which takes into consideration the flattening of the bevel.
It is thus an object of the invention to overcome the disadvantages of the known spectacle lens edge grinding machines and to design the transducer such that with a simple construction, independent of the atmosphere, the resulting soiling and optionally present deposits within the housing of the spectacle lens edge grinding machine, a sufficiently exact measuring result can be obtained. Furthermore, the measuring results should additionally take into consideration changes of the V-shaped bevel due to wear of the grinding wheel used for manufacturing the V-shaped bevel.